You have allowed push notifications from your browser for some dodgy sites. Disable all browser push notifications.
In Firefox: Go to Settings --> Privacy and Security --> Scroll to Permission block and click on the settings button for Notifications --> Click on Remove all websites
In Chrome: Go to Settings --> Privacy and Security --> Notifications Then block notifications for any site that you don't know https://omegle.onl/
In Safari: Choose Safari > Settings. Click Websites, then click Notifications. Deselect “Allow websites to ask for permission to send notifications.
If that does not help, consider resetting your browsers.